问AVAssetImageGenerator -获取错误代码-11800

EN

AVURLAsset *as = [[AVURLAsset alloc] initWithURL:url options:nil];
AVAssetImageGenerator *ima = [[AVAssetImageGenerator alloc] initWithAsset:as];
NSError *err = NULL;
CMTime time = CMTimeMake(0, 30);
CGImageRef imgRef = [ima copyCGImageAtTime:time actualTime:NULL error:&err];
UIImage *currentImg = [[UIImage alloc] initWithCGImage:imgRef];

callback(currentImg, err);

AVURLAsset *asset=[[AVURLAsset alloc] initWithURL:url options:nil];
AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
generator.appliesPreferredTrackTransform=TRUE;

CMTime thumbTime = CMTimeMakeWithSeconds(0,30);

AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef imgRef, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error){
    if (result != AVAssetImageGeneratorSucceeded) {
        NSLog(@"couldn't generate thumbnail, error:%@", error);
        callback(nil, error);
    }

    UIImage *thumbnail = [UIImage imageWithCGImage:imgRef];
    callback(thumbnail, nil);
};

CGSize maxSize = CGSizeMake(128, 128);
generator.maximumSize = maxSize;
[generator generateCGImagesAsynchronouslyForTimes:[NSArray arrayWithObject:[NSValue valueWithCMTime:thumbTime]] completionHandler:handler];

    NSDictionary *options = @{ AVURLAssetPreferPreciseDurationAndTimingKey : @NO };
AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:url options:options];
NSArray *keys     = [NSArray arrayWithObject:@"readable"];
[asset loadValuesAsynchronouslyForKeys:keys completionHandler:^() {

    AVAssetImageGenerator *generate = [[AVAssetImageGenerator alloc] initWithAsset:asset];

    NSError *err = NULL;
    CMTime time = CMTimeMake(1, 30);

    CGImageRef imgRef = [generate copyCGImageAtTime:time actualTime:NULL error:&err];
    UIImage *thumbnail = [UIImage imageWithCGImage:imgRef];

    dispatch_async(dispatch_get_main_queue(), ^{
        callback(thumbnail, err);
    });
}];